Added support for Rexster 2.4.0 Metrics

This updates Titan to use TinkerPop 2.4.0-SNAPSHOT.  

Support for Metrics in Titan is dependent upon these changes in Rexster 2.4.0: https://github.com/tinkerpop/rexster/pull/307

I was able to get the metrics to work by making `ReporterConfig` setup occur first -- I had to move `RexProRexsterServer` and `HttpRexsterServer` instantiation out of the `RextsterTitanServer` constructor and into the `start` method instead.  It seems to work fine, and I suppose it shouldn't cause an issue as long as `start` is only called once.

There was one issue in `TitanSpecificBlueprintsTestSuite` that I didn't know how to fix. This particular test should fail every time.

More discussion about Titan Metrics: https://github.com/thinkaurelius/titan/issues/268